Equisetum palustre

Equisetum palustre, the marsh horsetail, is a perennial herbaceous pteridophyte belonging to the division of horsetails (Equisetopsida). It is widespread in cooler regions of North America and Eurasia.

Description
Equisetum palustre has stems growing between 20-40 centimeters. The upright stems are usually scarcely branched with loose green leaf sheaths that have 5-10 narrow, dark teeth. The teeth are light at the edges. The lowest internode of the upright branches are much shorter than the leaf sheath of the stem.

The rough, furrowed stem is one to three mm in diameter with usually eight to ten ribs, in rare cases, four to 12. It contains whorled branches.

The spores are spread by the wind (anemochory) and have four long ribbon-like structures attached to them. The spores sit on strobili which are rounded on the top. Marsh horsetails often form runners, with which they also can proliferate vegetatively.

Taxonomy
Linnaeus was the first to describe marsh horsetail with the binomial Equisetum palustre in his Species Plantarum of 1753.

Ecology
Equisetum palustre is green from spring to autumn and grows spores from June to September. It grows primarily in nutrient-rich wet meadows. It is found in Europe and the circumpolar region up to mountainous heights. Its distribution is declining.

In Finland, it has benefited from human action and grows often in road and track sides, ditches and especially peat based fields and pastures.

A specific plant association in which E. palustre is found is the Juncus subnodulosus-Cirsium palustre fen-meadow.

Toxicity
Equisetum palustre is poisonous to mammals, most often reported as potentially fatal to horses, as it contains alkaloids palustrine and palustridiene, which destroy vitamin B1. According to Wink, Equisetum Palustre also contains thiaminase enzymes. It's also known to contain lesser amounts of nicotine. Many thiaminases, however, are denatured by heat, and some sources refer Equisetum palustre safe to eat in moderate amounts when properly cooked. In Finland, it used to lower the production of dairy when cows would eat them in place of other preferable fodder.